CSE 486/586 CSE 486/586 Distributed Systems Introduction Steve Ko Computer Sciences and Engineering University at Buffalo

CSE 486/586 Welcome to CSE 486/586 Why do you want to take this course? Some positive feedback of this course… –“(CSE 486/586) didn't only helped with understanding the concepts involved, but have also always given me something cool and interesting to talk about in interviews.” –“I am actually learning new things.” –“(CSE 486/586) literally got me a job.” Some negative feedback of this course… –“Projects are a bit too much on the difficult side.” –“The midterm came almost out of nowhere.” –“Stay away at all cost!” Are you ready? ;-) 2

CSE 486/586 Building a Distributed System “The number of people who know how to build really solid distributed systems…is about ten” –Scott Shenker, Professor at UC Berkeley The point: it’s hard to build a solid distributed system. So, why is it hard?...but first of all… 3

CSE 486/586 What is a Distributed System? 4

CSE 486/586 What is a Distributed System? A distributed system is a collection of entities with a common goal, each of which is autonomous, programmable, asynchronous and failure-prone, and which communicate through an unreliable communication medium. This will be a working definition for us. 5

CSE 486/586 Why Is It Hard to Build One? Scale: hundreds or thousands of machines –Google: 4K-machine MapReduce cluster –Yahoo!: 4K-machine Hadoop cluster –Akamai: 70K machines distributed over the world –Facebook: 60K machines providing the service –Hard enough to program one machine! Dynamism: machines do fail! –50 machine failures out of 20K machine cluster per day (reported by Yahoo!) –1 disk failure out of 16K disks every 6 hours (reported by Google) As we will learn, these come with: –Concurrent execution, consistency, etc. 6

CSE 486/586 OK; But Who Cares? This is where all the actions are! –What is the two biggest driving forces in the computing industry for the last 7-8 years? –It’s the cloud! –And smartphones! –They are distributed! Now --- it’s all about distributed systems! –Well…with a bit of exaggeration… ;-) 7

CSE 486/586 OK, Cool; How Am I Going to Learn? Textbook –Main: Distributed Systems: Concepts and Design, 5 th Edition (Coulouris, Dollimore, Kindberg, Blair) –Optional: Distributed Systems: Principles and Paradigms, 2 nd Edition, (Tanenbaum, Van Steen) Lectures (Non-graded) HW assignments Programming assignments Exams 8

CSE 486/586 What Am I Going to Build? A “starter” project: PA1 –This will be out today and due next Monday. A distributed key-value storage (based on Amazon Dynamo) on Android in multiple stages Individual submission 9

CSE 486/586 Important Policies Late submissions only allowed for one day –20% penalty –The deadlines are on Friday, and we don’t count weekends, so technically you have 3 more days. Regrading –If requested, the entire work will be regraded No “I” No makeup exam No grade negotiation 10

CSE 486/586 I Have a Confession to Make… I have a split personality disorder. –Jekyll –Hyde Most of you (I expect) will just see my Jekyll’s side. If you… –work with good ethics, –respect others on Piazza, office hours, etc., –follow class and submission rules, –and generally use common sense and are a good citizen in the class. Some of you might see my Hyde’s side. If you… –copy other people’s code or exams, –try to negotiate your way in the class, –generally are not such a good citizen in the class. 11

CSE 486/586 Academic Integrity Policies Academic integrity: exams, HW, and code –Copying others’ code: no –Copying from other sources (the Web, books, etc.): get permission –Exceptions: (copy freely, but mark clearly that you copied) – (generally OK to see how things get done; but do not copy and paste.) –If found, the incident will be reported to the university. Will use an automatic similarity checker. –When similar submissions are found, both will get F for the entire semester. Please be careful when using an online code repository, e.g., GitHub, BitBucket, etc. 12

CSE 486/586 How Can I Reach the Teaching Staff? Steve: 304 Davis –Lectures (MWF 1:00pm-1:50pm) –Office hours (MWF 2pm-3pm) TAs –Office hours: TBD –Undergrad recitations: Typically only when a new PA is out. –Please do not expect that the TAs will stay more than the announced office hours. Use Piazza ( instead of , mailing list, blog, etc. –The teaching staff will not have any activity during weekends and holidays. –Signup link: 13

CSE 486/586 Background Required You must have some background in different topics. OS concepts –Threads, processes, synchronization (e.g., locks, semaphores), etc. Networking concepts –IP, DNS, NAT (e.g., private IPs vs. public IPs), TCP, etc. System programming experiences –Programming experiences with sockets, processes, threads, synchronization primitives, file I/O, etc. –Experiences with setting up environment variables, using regex, scripting (e.g., bash, python, etc.) Programming environment –Linux or Mac 14

CSE 486/586 Background Check: PA1 Programming Assignment (PA) 1 –Use this as a background check. –If you can finish this in a week all by yourself, then you are ready to take this class. –See for yourself! –Due on next Monday (2/2) 11:59:59 am. SimpleMessenger on Android –Overall, need to implement a chatting app. –Need to set up Android programming environment. –Need to use sockets. –Need to understand the code provided. –Need to read Android tutorials and understand them. –Need to understand and use Android APIs. 15

CSE 486/586 What Exactly Am I Going to Learn? Distributed Systems 10 Questions! Course goal: answering 10 questions on distributed systems –At the end of the semester, if you can answer only 10 questions about distributed systems, you’ll probably get an A. –Easy enough! What are those questions? –Organized in 6 themes –1~2 questions in each theme –A few (or several) lectures to answer each question 16

CSE 486/586 What Exactly Am I Going to Learn? Introducing… Hydie! 17

CSE 486/586 Theme 1: Hint 18 What’s up? Hey!

CSE 486/586 Theme 1: Communications Q1: how do you talk to another machine? –Networking basics Q2: how do you talk to multiple machines at once? –Multicast Q3: can you call a function/method/procedure running in another machine? –RPC 19

CSE 486/586 Theme 2: Hint 20 I’m shaking my tail. What? I’m doing it too! I thought I was doing it…

CSE 486/586 Theme 2: Concurrency Q4: how do you control access to shared resources? –Distributed mutual exclusion, distributed transactions, 2- phase commit, etc. 21

CSE 486/586 Theme 3: Hint 22 I want to shake my tail. No, I don’t want to. OK No way!

CSE 486/586 Theme 3: Consensus Q5: how do multiple machines reach an agreement? –Time & synchronization, global states, snapshots, mutual exclusion, leader election, paxos Bad news: it’s impossible! –The impossibility of consensus 23

CSE 486/586 Theme 4: Hint 24 Who has a brain? I do. I don’t.

CSE 486/586 Theme 4: Storage Management Q6: how do you locate where things are and access them? –DHT, DFS 25

CSE 486/586 Theme 5: Hint 26 zzz… I have a feeling that something went wrong…

CSE 486/586 Theme 5: Non-Byzantine Failures Q7: how do you know if a machine has failed? –Failure detection Q8: how do you program your system to operate continually even under failures? –Replication, gossiping 27

CSE 486/586 Theme 6: Hint 28 We’re under attack!

CSE 486/586 Theme 6: Byzantine Failures Q9: how do you deal with attackers? –Security Q10: what if some machines malfunction? –Byzantine fault tolerance 29

CSE 486/ Acknowledgements These slides heavily contain material developed and copyrighted by Indranil Gupta at UIUC. The material was originally developed for courses CS425/CSE424/ECE428 at UIUC.